This information was taken from White-tailed Deer: Ecology and Management. It is A Wildlife Management Institute Book, Compiled and Edited by Lowell K. Halls, published by Stackpole Books, copyright 1984 by the Wildlife Management Institute.

Photperiodism

Except near the equator, the rutting season is tied to photoperiodism. A diminishing ration of daylight to darkness triggers the start of the reproductive cycle. Photoperiodism serves as a time-giver for the inherent (endogenous) rhythm, the so-called "biological clock." Deer shifted from one hemisphere to another adjust their breeding season to the prevailing photoperiod (Marshall 1937).

Since photoperiodism is related to latitude, the rut progresses more or less as a continuum from November in the North to January or February in far southern ranges. Variation within a region possibly is due to genetic differences (Ransom 1966a) or hybridization (Haugen 1959, Adams 1960).

In northern latitudes, antler growth begins in spring, with the increasing length of daylight. Goss (1969a, 1969b) induced four complete sets of antlers in one year in Sika deer by subjecting the deer to photoperiods that simulated the natural annual cycle. Bucks exposed to equal periods of daylight and darkness failed to grow new antlers during the three year duration of the experiment.

Male Reproductive Patterns

Robinson et al. (1965) described a three-phase testicular cycle, in Texas whitetail bucks, consisting of (1) primary development, (2) full production and (3) resting stage. These phases were associated with the onset of antler growth, the shedding of velvet and antler drop, respectively. Relative development of the seminal vesicles lagged slightly behind that of the testes and exhibited a sharper peak. Thus the seminal vesicles more accurately reflected the actual breeding period than did testes size. Mararchi et al. (1977a) indicated that season fluctuations in testes weight probably are caused by increased and decreased activity of the seminiferous tubules. Numbers of testicular sperm were correlated closely with counts in the epididymus. These results suggest that rising androgen levels may be necessary for sperm formation or maturation. Testosterone might be involved more in initiating than in maintaining spermatogenesis. The follicle-stimulating hormone provides the stimulus for spermatozoan production (Mirarchi et al. 1978).

Lambiase et al. (1972) noted that whitetail sperm production extended from mid-August through March. Number of sperm per ejaculation increased through October, peaked in mid-November, dropped almost in half by mid-December and declined at a slower rate thereafter. Maximum sperm counts were in the billions (3.4 x 10 to the 9th power) per ejacualate. Sperm production and testes size are greatest in older males. However, buck fawns are sexually mature and, given the opportunity, can successfully impregnate females.

Testosterone governs the course of antler development. If a buck is castrated while its antlers are in velvet, those antlers are retained, but never harden or lose their velvet. If a buck is castrated after shedding its antlers, the antlers regrow the next year, with the velvet being retained. An animal castrated after the velvet is shed loses its antlers within a week (Wislocki et al. 1947). The pattern of antler casting and regrowth probably involves an interplay between testosterone level and the antler-growth stimulus secreted by the pituitary in response to photoperiodism (Whitehead and McEwan 1973). Mirarchi et al. (1978) believe that prolactin also influences antler regeneration and growth. The role of the growth hormone in this regard still is uncertain.

Testosterone levels are correlated with progressive antler growth and hardening and the shedding of velvet (McMillin et al. 1974). Testosterone concentration and testicular volume begin to increase in August, peaking in October and dropping to low levels from December through July. Peak testosterone output in October implies that this hormone is instrumental in bucks establishing their dominance hierarchy prior to the rut. The superior (dominant) buck probably breeds most of the does within his home range.

Bucks in good physical condition retain their antlers longer than do those in poor vigor (Ozoga and Verme 1982a). Antler development is affected greatly by diet, and its general conformation is dictated by heredity. Antler size in autumn, especially among yearling cervids, may provide a useful index of the animals' earlier (late winter) physical condition (Taber 1958). Experiments in Pennsylvania (French et al. 1955, Cowan and Long 1962) indicated that young bucks had the best antlers and the heaviest body weight when fed a complete ration. Food restriction during winter, however, did not appreciably reduce antler size when the animals received an adequate diet during spring and early summer. Body growth took precedence over antler formation.

While large antlers are important for successful courtship among adult bucks, a strong body may be more essential to establishing a male's dominance. Antler development, pelage change and antler shedding were delayed when yearling bucks were on a restricted diet for up to 10 weeks beginning in mid-March (Long et al. 1959). These results emphasized the value of proper nutrition when antler growth commences. A delayed, cool spring, for example, could prove detrimental to antler development.

The rut is a very strenuous time for bucks. Physical debilitation at this time could adversely affect subsequent antler development and social rank for bucks past their prime, particularly those on marginal ranges. Perhaps because the breeding season is so taxing, bucks generally have a shorter life-span than do does even in lightly hunted areas or refuges (Ozoga 1969).

Marshall, F. H. A. 1937. On the change over in the oestrus cycle in animals after transference across the equator, with further observations on the incidence of the breeding season and the factor controlling sexual periodicty. Proc. Royal Soc. London, Ser. B. 122:413-428.

Wislocki, G. B., J. C. Aug, and C. M. Waldo. 1947. The effects of gonadectomy and the administration of testosterone propionate on the growth of antlers in male and female deer. Endocrinology 40(3):202-224.

If anyone is really interested in white-tailed deer, that book is the DEFINITIVE text when it comes to the critters. Best I can remember, it was $65-70 though. It's also a pretty hefty book, holding 793 pages of just text. When you compile that with all the pages with pictures, the references, index, etc., it's close to 4" thick. The great thing though is that it will tell you anything and everything you ever wanted to know about white-tailed deer. About the only thing that may be missing from it is all of the current stuff going on with chronic wasting disease.